1. Technical Field
The present invention relates to a fluid ejection device and to a cleaning control method for recovering a fluid ejection head such as an inkjet head from a faulty fluid ejection state, and relates more particularly to a fluid ejection device and a cleaning control method that run a nozzle check to determine the recovery condition of the nozzles after cleaning.
2. Related Art
The nozzles of an inkjet head used in an inkjet printer can become clogged as a result of bubbles or an increase in the viscosity of ink or other fluid droplets inside the nozzles, or the adherence of foreign matter, resulting in the clogged nozzles being unable to eject fluid droplets. Nozzles may also become partially clogged so that a sufficient volume of ink cannot be ejected. Because print quality will drop if printing is attempted using an inkjet head that has nozzles that are not ejecting correctly (referred to below as “faulty nozzles”), cleaning is required at a regular interval or specific time to restore any faulty nozzles to normal operation.
Japanese Unexamined Patent Appl. Pub. JP-A-2009-208420 teaches an inkjet printer that executes a nozzle check to determine if any nozzles of an inkjet head are faulty, and then runs a cleaning process based on the result of this nozzle check. After cleaning the nozzles based on the result of the nozzle check and the number of faulty nozzles, the inkjet printer described in JP-A-2009-208420 confirms if the nozzles were recovered from the deficient discharge state by running the nozzle check again. If a faulty nozzle is detected, cleaning is repeated, and this process may repeat to a maximum four cleaning operations.
The cleaning operation in JP-A-2009-208420 may be accomplished by an ink suction operation that caps the nozzle surface with a head cap to create a sealed space and then applies suction to this closed space to produce negative pressure around the nozzles and draw ink from the nozzles; a flushing operation that discharges ink from the nozzles in a non-printing operation; or a wiping process that mechanically wipes the nozzle surface with a wiper blade, for example.
When an ink suction operation is used as the cleaning operation, ink continues to flow through the ink supply path and the inkjet head to the nozzle side for some time after cleaning ends, and bubbles contained in the ink may be pulled again to the nozzle side, thus inducing the formation of a faulty nozzle again (this phenomenon is referred to as “induction” herein). More specifically, new faulty nozzles may be produced in the time it takes for ink flow to stabilize after the ink suction operation ends.
More particularly, if suctioning the closed space starts with the ink supply path for supplying ink to the head choked off by a choke valve mechanism, and the ink supply path is then unchoked and additional suction is applied in a choked suction operation that suddenly suctions ink, bubbles created by this choked suction operation sometimes result in the formation of new faulty nozzles.
When new faulty nozzles may thus be formed by induction after cleaning, the results of a nozzle check performed before the ink flow stabilizes will be imprecise. As a result, the need for cleaning to achieve the print quality required by the user, and the content of the required cleaning operation, cannot be accurately determined.
The printer taught in JP-A-2009-208420 inspects the condition of the nozzles after nozzle cleaning by means of a nozzle check, and cleans again if a faulty nozzle is found. However, JP-A-2009-208420 does not address the actual timing of this nozzle check, and a drop in the accuracy of the nozzle check caused by induction is not considered. As a result, faulty nozzles formed by induction may not be detected by the nozzle check, and the number of faulty nozzles present after cleaning ends cannot be accurately determined. Whether or not cleaning resulted in a complete recovery state in which there is not even a single faulty nozzle cannot be accurately known. Cleaning also cannot be optimally applied to efficiently achieve a recovery condition meeting the user's needs.